Apparatus for turning and transferring sheet metal

ABSTRACT

A sheet metal such as a tin plate having the property of being attracted by magnetic force and having one surface printed or coated is transferred from a drying furnace with said surface facing downwards and is received by a first transfer means and then passed to the second transfer means, each transfer means having two pulleys and a single endless belt suspended therebetween. The sheet metal moves forward and turns back with the belt as it does and proceeds substantially along the lower path of the belt as it is attracted by the electromagnet mounted along said path of the belt. When the sheet metal arrives at a predetermined position, the electric current of said electromagnet is interrupted by means of a sensing means attached to said electromagnet, whereby the sheet metal drops down upon a discharge means provided below said path and thereafter it is passed to the next step with said printed or coated surface facing upwards.

nited States Patent 1 [111 3,795,301 Sugitani Mar. 5, 1974 APPARATUS FOR TURNIIN IG AND Primary Examiner-Richard E. Aegerter TRANSFERRING SHEET .METAL [7 5] lnventor: Ejyo Sugitani, Kuniyoshida, Japan {73] Assignee: Dawa Can Company, Limited,

Chuo-ku, Tokyo, Japan [22] Filed: May 10, 1972 [21] Appl. No.: 252,088

[52] US. Cl. 198/20 R, 198/33 AD, 198/41 [51] Int. Cl. 365g 47/00, 865g 43/00 [58] Field of Search 198/134, 41, 33 AD, 20, 102, 198/41; 271/63 A [56] References Cited UNITED STATES PATENTS 1,998,912 4/1935 Troy 198/84 3,523,602 8/1970 Mojden.... 198/41 3,602,359 8/1971 Miya 198/41 3,633,731 l/1972 Jones 271/74 [5 7 ABSTRACT A sheet metal such as a tin plate having the property of being attracted by magnetic force and having one surface printed or coated is transferred from a drying furnace with said surface facing downwards and is received by a first transfer means and then passed to the second transfer means, each transfer means having two pulleys and a single endless belt suspended therebetween. The sheet metal moves forward and turns 'back with the belt as it does and proceeds substantially along the lower path of the belt as it is attracted by the electromagnet mounted along said path of the belt. When the sheet metal arrives at a predetermined position, the electric current of said electromagnet is interrupted by means of a sensing means attached to said electromagnet, whereby the sheet metal drops down upon a discharge means provided below said path and thereafter it is passed to the next step with said printed or coated surface facing upwards.

4 Claims, 6 Drawing Figures PATENTEDHAR 5M4 SHEET 10F 2 FIG. 2

PATENTEDHAR 5 I974 SHEU 2 0F 2 Y-Y section X-X section X-X section APPARATUS FOR TURNING AND TRANSFERRING SHEET METAL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of apparatus for transporting magnetizable articles.

2. Description of the Prior Art FIG. 1 is a schematic view illustrating one embodi ment of an apparatus heretofore used adapted for receiving a plurality of sheet metals, such as tin plates, with the printed or coated surface facing downward after they are successively passed out from a drying furnace with said printed or coated surface facing forward, and transporting the same to the next step.

The sheet metal A is transferred by a conventional method from the drying furnace (not shown) with said surface downward to the endless belt of the conveyortype middle transfer means 101 provided near the outlet of said furnace, and then proceeds toward a rotary wheel I04 provided adjacent to said transfer means. This rotary wheelis provided with many wickets 105 radially mounted on the shaft 102, and allowed to rotate in the direction of an arrow Q matching with the interval of the sheets being transferred so that one said wicket may receive one sheet metal. The sheet metal A received by one wicket 105 from said transfer means is caused to rotate, and when it rotates 180, it is then passed to another transfer means 103 with said printed or coated surface upward. Said transfer means 103 is arranged in a position opposite to said middle transfer means 101 with respect to said wheel 104 and rotates in the same direction as that of the means 101.

In the aforesaid conventional method, however, the sheet metal does not always come out of the drying furnace with a predetermined constant interval. It is thus difficult to register the rotation of the rotary wheel with the interval of the sheet metals being transferred. Particularly when the number of sheets transferred per unit time increases, it often happens that two sheets enter into one wicket or the sheet collides with the wicket and is bent thereby; if not, the printed or coated surface of the sheet will be injured or worn out by the wicket. In addition, there is a disadvantage that the space occupied for the operation is increased since the two transfer means and the rotary wheels are lined in series.

SUMMARY OF THE INVENTION This invention is directed to overcoming the aforementioned disadvantages which are encountered in the conventional rotary wheel system.

According to the instant invention, the rotary wheel of the aforedescribed apparatus is replaced by a unique apparatus which comprises two pulleys, the forward one of which is provided with means to attract the sheet metals, an endless belt suspended between said pulleys, one or more electromagnets provided along the under side path of said belt and a sensing means capable of eliminating the magnetic force of said electromagnet.

In addition thereto, a middle transfer means and other transfer means of the conventional type can be used.

It is therefore an object of the invention to receive sheet metals capable of being attracted by magnetic force one by one accurately from the drying furface even when the interval of the sheets being transferred is not constant. It is another object of the invention to turn the sheet metals and pass the same to the next step without injuring the printed or coated surface thereof. It is still another object of the invention to conduct such method within an operation area which is narrower than that of the conventional method.

These and other objects and advantages of the pres- 'ent invention will become apparent from the following detailed description and accompanying drawings wherein a preferred embodiment is shown.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view illustrating the conventional system of turning sheet metals by means of a rotary wheel.

FIG. 2 is a schematic view illustrating one embodiment of turning sheet metals according to the method of the present invention.

FIG. 3 is an enlarged sectional side view taken along III-III of FIG. 2 illustrating one embodiment of the second pulley of the second transfer means according to the apparatus of the present invention showing arrangement of the permanent magnets.

FIG. 4 is a perspective view partly broken illustrating the major part of one embodiment of the apparatus of the present invention, in which means to support pulleys, electromagnets and sensing means are omitted.

FIG. 5 is a schematic view showing arrangement of electromagnets along the underside of the magnet belt when the endless belt of the second transfer means is replaced by said magnet belt according to the invention wherein (a) is one example of a side view and two sectional views taken along X-X and YY, respectively, and (b) is another example of a side view and a sectional view taken along X-X thereof, in which means to support electromagnets and roller cases are omitted.

DESCRIPTION OF THE PREFERRED EMBODIMENT One preferred embodiment is further described with respect to FIG. 2. A sheet metal A which has the property of being attracted by magnetic force and which is coated or printed on one surface thereof is caused to stand substantially vertically with said surface facing forward between the wickets 5 on the chains 4 for transferring the sheet metal. Said frames are mounted at the interval of one pitch of the chain. The sheet is allowed to pass inside the drying furnace (not shown) leaning on the wicket and finally carried out of the furnace, and in the meantime the ink or paint applied to the surface of the sheet metal is dried and secured thereon. In FIG. 2, the reference numeral 1 is a sprocket for driving said chains 4 at the outlet of said furnace; 2 and 3 are the respective sprockets defining the upper and lower paths of said chains 4; and the arrow P indicates the moving direction of said chains 4. As the chains 4 proceed in the direction P, the sheet metal 4 moves therewith. When the chains 4 begin to move around the sprocket I, the sheet metal A leans on the preceding wicket 5. As said wicket 5 reaches the horizontal position, said sheet metal A is carried to the first transfer means with said printed or coated surface downward.

The first transfer means which corresponds to the middle transfer means 101 in FIG. I is provided in the vicinity of the chains 4 and composed of two pulleys 6, 7 and an endless belt 8 suspended in parallel therebetween. The pulley 6 is a rearward one and the pulley 7 is a forward driving one. The belt 8 moves in the same direction as that of the chains 4. The upper path 8 of the belt 8 should preferably be aligned with the extention line of the wicket which has rotated down to said horizontal position. The sheet metal A leaning on the wicket 5 which has rotated down to said horizontal position is transferred from the wicket 5 to the upper path 8' of the belt. A suitable number of such transfer means are provided in parallel depending upon the width and flexibility of the sheet metal A and the width of the belt so that the sheet metal A may be supported and conveyed horizontally.

The way of carrying the sheet metals A one by one between each two wickets on the chains 4 is not described herein since it is substantially the same as the conventional method. The same is true with the relation between the position of the wicket and that of the first transfer means and with the structure of the wick- The sheet metal A is then carried from the first transfer means to the second transfer means. The latter means is positioned near the forward driving pulley 7 of the first transfer means and possessed a first or rearward pulley 9 the apex of which is substantially as high as that of pulley 7, a and the second or forward driving pulley 10 which is provided in the preceding position and an endless belt 11 suspended between these two pulleys. The belt 11 moves in the same direction as that of the belt 8 of the first transfer means and at least the lower path 11 is positioned such that it may be substantially horizontal. Moreover, the second pulley 10 is provided with a means to attract the sheet metal A so that the sheet metal can be kept on the belt 11 so as to turn and move along with said pulley 10. An example of such means is one or more permanent magnets embedded in the periphery of the pulley 10 in a concentric relation therewith as shown in FIG. 3. In FIG. 3, the numeral 10 is the pulley made of aluminum alloy, in the periphery of which are embedded permanent magnets 12 concentrically within the pulley at suitable intervals. On both sides of the magnets, annular rings 22 made of iron are mounted. Reference numeral 11 designates the belt. In FIG. 3, the permanent magnets are shown as arranged in two lines but the number ofsuch lines as one, two or three, etc., depends upon the size, thickness and material ofthe sheet metal A used. The important thing is that the attracting means should have power enough to attract the sheet metal without dropping the latter and during its travel around the pulley.

As set forth above, the sheet metal A proceeds with the belt around the pulley 10 as attracted thereto by means of said attracting means. If the plastic deformation occurs on the sheet metal during the above course, it becomes impossible to work the same in the next step. In order to prevent such plastic deformation, the size of the pulley must be determined by taking into account the thickness, width, length and material of the sheet metal used. The dimensions of the second trans fer means can be determined depending upon the conditions of the sheet metal A and the belt 11 as is the case with the first transfer means.

The sheet metal A after turning around the second pulley 10, comes into the lower path 11. If there is nothing attracting the sheet metal with the lower path of the belt, the sheet metal will naturally drop down. In order to avoid this, there are provided one or more electromagnets 13 near the pulley 10 and above said lower path of the belt with a slight space between the magnets and the belt, which magnets will make it possible to allow the metal sheet to proceed with the belt even when the metal sheet comes out of reach of the attracting power of the second pulley.

It is preferable that the electromagnets 13 are mounted as near the second pulley 10 as possible. In this case, when the sheet metal A is not subjected to the attracting power of the second pulley, it will have already come under the influence of the attracting power of the electromagnets. Consequently, there is no fear that the sheet metal will drop or become suspended from the belt, and thus they are allowed to proceed with the lower path of the belt very smoothly. It is contemplated according to this invention that one or more minor auxiliary attracting means 14 such as permanent magnets or vacuum attracting means be provided between the second pulley 10 and the electromagnet 13 depending upon the shape, structure and capacity, etc., of the electromagnet. The structure of the apparatus of the invention will be better understood by FIG. 4 showing the major part of the apparatus. In FIG. 4, however, means of supporting each pulley and electromagnets or auxiliary attracting means which are to be set slightly above the lower path 11', and the like are omitted for simplification, since they can be those which are conventionally used. Also in FIG. 4, the first transfer means, second transfer means and the electromagnet are shown as three units, respectively, but it is to be understood that the number of such means is not limited thereto. For example, the electromagnets 13 do not have to be placed above the entire length of the lower path of the belt 11 and can instead be placed only above the right and left ends of said path omitting the middle part thereof so long as the magnets are strong enough to continuously attract the sheet metal A. In FIG. 4, the second pulley 10 of the second transfer means is shown as one considerably greater in size than the first pulley 9 and therefore the slope of the upper path of the belt 11 is relatively steep, providing the advantage that the second transfer means can be made compact with respect to length. If, however, the slope is toosteep, there is a danger that the sheet metal A may slide down. As a countermeasure thereto, a suitable number of permanent magnets shown as the numerals 16 in FIG. 2 are provided slightly below the upper path of the belt 11. The supporting means of such magnets are not shown for simplification.

It is preferable that the electromagnet 13 is longer than the sheet metal A. The slight space between the lower surface of the electromagnet and the inner surface of the belt opposite thereto is necessary because the sheet metal A is attached to the belt but not to the electromagnet, which makes it possible for the sheet metal to proceed with the belt.

In FIGS. 2 and 4, the reference numeral 15 indicates a sensing means provided near the electromagnet 13, which means is adapted for sensing the access of the sheet metal and being actuated thereby so as to eliminate the attracting power of the electromagnet 13 when or after the sheet metal A travelling with the belt along the lower path of the second transfer means under the influence of the attracting power of the electromagnet 13 comes out of reach of the attracting power of the second pulley It) with respect to the rear end thereof.

This sensing means 15 does not have to be placed on each belt line and one means will suffice per the whole electromagnet.

As the sensing means, various kinds of operating switches for control may be used. The non contact adjacent switch is one of the optimum ones for the purpose since it has no movable mechanical part and has a semipermanent life. The position of the detecting head or sensor of said switch will vary with the length of the metal sheet A, the distance between the electromagnet 13 and the second pulley It and the distance within reach of the attracting power of the second pulley over the sheet metal, but in short, it can be positioned such that when the sheet metal A travelling along the lower path 11' reaches the position where it is not subjected to the attracting power of the second pulley 10 or other means than the electromagnet 13, it will sense the approach of the fore end of the sheet metal and be actuated thereby to interrupt the electric current of the electromagnet 13.

When the sheet metal arrives at the above position and the means 15 is actuated to eliminate the magnetic force of the electromagnet 113, the sheet metal having no supporting means is allowed to drop down from the belt with the printed or coated surface upward. A conveyor-type discharging means 17 is provided under the lower path 1 l of the belt in order to receive the dropping sheet metal and convey the same to the next step. This discharging means 17 corresponds to the means 103 in FIG. 1 and comprises, for example, a pulley 18 provided below the first pulley 9 of the second transfer means, an endless belt 19 (not shown) driven thereby and another pulley provided opposite thereto.

This belt l9 moves in the same direction as that of the belts 8 and II in the first and second transfer means, respectively. The number of sets is shown as two in FIG. 4 but the number can vary therefrom as previously explained. The distance between the lower path ll of the second transfer means and the upper path of the belt 19 of the discharging means 17 must be such that the sheet metal A carried with the belt 119 is not substantially subjected to the attracting power of the energized electromagnet 13 and the second pulley l0, and if any, the permanent magnet 14 and the like. Moreover, the belt 19 and the endless belt 11 of the second transfer means must be driven at a rate not less than that of the transfer speed of the sheet metal in the first transfer means in order to prevent an accident for example two or more sheet metals become overlapped and transferred to the next step, which accident is caused by that before the preceding sheet metal is car ried away the subsequent sheet metal or metals drop down thereon. If so, the sheet metals can he carried one by one with accuracy to the next step even if the transfer interval of the sheet metals is not constant so long as the length of each sheet metal is substantially equal.

Alternatively, it is possible that the endless belt 11 of the second transfer means of the present invention is the magnet belt.

if the endless belt III is the magnet belt, the auxiliary attracting means 114 and 16 shown in FIG. 2 become unnecessary. In addition, there is an advantage that the power of the attracting means of the second pulley 210 can be made smaller than that of the case of using the non-magnet belt.

As for the degree of the attracting power of the magnet belt lll, there are two cases. One case is that said attracting power is so strong that the sheet metal can be sufficiently attracted by the belt and proceed along the lower path ill without the aid of the above mentioned electromagnet I3, and the other case is that said attracting power is not so strong and the sheet metal can not be attracted thereby and can not proceed along the lower path 11' without the aid of the electromagnet 13. Since the latter case is the same as when the endless belt 11 is the non-magnet belt, further explanation thereof will be unnecessary. In the former case, however, it is necessary that the structure of the electromagnet 13 must be changed to a peculiar one. That is because when the fore end of the sheet metal A pro ceeding along the lower path ill of the endless belt I l is sensed by the sensing means 15 whereby the attracting power of the electromagnet 13 is going to be elimi nated, the sheet metal A should be in the condition that it is not subjected to the attracting power of the magnet belt 11 any longer and yet not prevented from travelling farther on.

FIG. 5 shows one example of the electromagnets which are intended to meet the above requirements. In FIG. 5a the bottom of the electromagnet I3 to be mounted above the lower path 11 of the magnet belt is shaped into a U type so that it can span the belt and moreover a group of small rollers 20a 20d 20n is rotatably mounted on the lower and outer side of the magnet 13 along the direction of the movement of the belt. In this case the lower surface of the rollers is ar ranged such that they are downwardly projected slightly beyond the lower surface 13 of the right and left projected parts of the electromagnet 13. When the sheet metal A attracted and carried by the belt smoothly enters under the electromagnet l3 and proceeds a little farther whereby the sensing means is actuated so that the electric current may be interrupted, the sheet metal must be placed apart from the belt to such an extent that it is not subjected to the attracting power of said belt any longer lest it should be prevented from dropping down. Where the sheet metal A begins to come under the electromagnet 13 shown as line YY in FIG. 5, the lower surface 13' of the electromagnet 13 is caused to lie at least at the same level as, and preferably at a higher level than, that of the lower surface of said belt, and then said surface 13' is caused to project downward gradually from the lower surface of said belt. In order to allow the sheet metal A to enter smoothly under the magnet, a group of the small rollers is arranged as mentioned hereinbefore. In addition, these rollers should be arranged such when at the time that the fore end of the sheet metal A approaches the aforesaid sensing means 15 whereby it is actuated to interrupt the electric current of the electromagnet 13, a space is formed between the sheet metal and the belt to the extent that the magnetic power is no longer exerted over the sheet metal or that the sheet metal is attracted toward the roller only by the magnetic power of the electromagnet.

In FIG. 5a, the distance d in the X-X section between the lower path 11' of the belt and the sheet metal A is one whereby the sheet metal is not subjected to the attracting power of the belt. Since in the XY zone of FIG. 5a the distance between the lower path ll of the belt and the sheet metal A is smaller than said d," the sheet metal A is attracted by both the belt and the electromagnet. On the other hand, in the right hand of the line XX, the sheet metal A is not substantially subjected to the attracting power of the belt. Consequently, the sensing means 15 is set in such a position that it is actuated when the sheet metal A enters into the right hand of the XX line where the sheet metal is ready to drop if the power of the magnet 13 has only to be interrupted.

As for the relation of the positions of the roller, the electromagnet and the belt, it is obvious from the sectional view that at least in the right hand of the XX line the lower surface 13' of the electromagnet is situated below the belt while the lower surface of the roller is below the lower surface of the electromagnet.

The position of said sensing means 15 and that of the line XX are co-relative. Thus in case that the latter position is stationary the former position can be determined depending upon the length of the sheet metal A, while in case that the former position is stationary the position of the line XX of the electromagnet with respect to the belt can be changed depending upon the length of the sheet metal.

Also in FIG. a, the rollers are shown as attached directly to the electromagnet 13, but FIG. 5b shows an example in which the rollers are set apart from the electromagnet 13 in the interior and lower part of a case 21 covering said electromagnet wherein the relation between lower path 11' of the belt and the electromagnet 13 is determined as mentioned above.

In FIG. 5, one row of rollers is respectively mounted on both longitudinal sides of one electromagnet. However, where three of such electromagnets are used in parallel as in FIG. 4, such one row of rollers can be respectively mounted on both outer sides of each outermost electromagnet, that is, two rows of rollers are set in total with respect to one set of electromagnets. The number of groups of rollers can thus be determined depending upon the weight of sheet metals, etc., as the case may be.

In the second embodiment as mentioned above, the sheet metal A entering the second transfer means from the first transfer means proceeds as attracted by the magnetic force of the belt, comes around the second pulley by virtue of the attracting power of the belt and the second pulley and enters the lower path 11' of the belt. As this belt has a magnetic force sufficient to attract the sheet metal A by its own power, the sheet metal A can proceed with said belt without dropping down even if the second pulley I0 is sufficiently apart from the electromagnet 13. The sheet metal is then brought under the electromagnet 13, proceeding farther on while subjected to the magnetic force of said belt and finally attain the condition where it is not substantially subjected to the effect of the magnetic fore of the belt. Then the sensing means 15 is allowed to operate by sensing the approach of the force end of the sheet metal A, whereby the sheet metalleaves the electromagnet which has already lost its attracting power by means of the sensing means, drops on the belt 19 of the discharging means 17 and is conveyed to the next step.

Even ifa part of the sheet metal, for example, its rear part or thereabout is still within such a region that it is subjected to the magnetic force of the belt, it can be said that the sheet metal A is, as a whole, under the condition that it is not subjected to the attracting power of said belt so long as the attracting power of the belt is not enough to prevent the sheet metal from dropping down.

I claim:

1. An apparatus for turning and transferring a sheet metal having a printed or coated surface which comprises (l) a first transfer means to receive the sheet metal with said surface down and transferring the same to the next step, said sheet metal having been passed from a drying furnace and having a property of being attracted by magnetic force, (2) a second transfer means which is composed of (a) first pulleys provided near the first transfer means, the top surface of the forrner being substantially equal to that of the latter, (b) second driving pulleys provided with attracting means, said means allowing endless belts to attract said sheet metal and allowing said sheet metal to travel with said belts and (c) the endless belts suspended between these pulleys, a lower path thereof being substantially flat, said second transfer means being adapted for receiving the sheet metal from the first transfer means and allowing the same to proceed and turn at a rate not less than that of the transfer speed of the sheet metal in the first transfer means, (3) electromagnets provided near said second pulleys and along and above the lower path of the endless belt of the second transfer means, said electromagnets being adapted for attracting said sheet metal and permitting said sheet metal to proceed with said belts, (4) at least one sensing means provided adja cent said electromagnets adapted for being actuated when at least the rear end of the sheet metal reaches a position where it is not substantially subjected to the attracting power of said second pulleys and thereby eliminating the attracting power of said electromagnets and (5) discharging means provided below the lower path of the endless belts of said second transfer means and adapted for carrying said sheet metal to the next step at a rate not less than that of the transfer speed of the sheet metal at the first transfer means, said sheet metal having been separated and dropped from said belts as a result that said electromagnets have lost the attracting power by the actuation of the sensing means, the space or distance between said discharging means and the lower path of said endless belts being such that the attracting power of said electromagnets can not be substantially exerted over the sheet metal which has dropped down on said discharging means.

2. An apparatus according to claim 1 in which the attracting means of the second pulleys at the second transfer means are permanent magnets provided in the periphery of said pulleys.

3. An apparatus according to claim 1 in which said sensing means is at least one non-contact adjacent switch.

4. An apparatus according to claim 1 in which the endless belts of the second transfer means are the magnet belts; the electromagnets provided along the lower path of the belts have, at least as a whole, one row of small rollers on each outer side thereof along the direction of travel of said belts, said rollers being capable of rotating on the sheet metal and forming a space between said sheet metal and said belts, said gap being such that the mere magnetic force of said belts is not enough to keep said sheet metal attracted thereto; and the sensing means is adapted for being actuated and eliminating the attracting power of said electromagnets when said sheet metal reaches the condition that it cannot be kept attracted by the belts by the single magnetic force of the belts.

l =l I 

1. An apparatus for turning and transferring a sheet metal having a printed or coated surface which comprises (1) a first transfer means to receive the sheet metal with said surface down and transferring the same to the next step, said sheet metal having been passed from a drying furnace and having a property of being attracted by magnetic force, (2) a second transfer means which is composed of (a) first pulleys provided near the first transfer means, the top surface of the former being substantially equal to that of the latter, (b) second driving pulleys provided with attracting means, said means allowing endless belts to attract said sheet metal and allowing said sheet metal to travel with said belts and (c) the endless belts suspended between these pulleys, a lower path thereof being substantially flat, said second transfer means being adapted for receiving the sheet metal from the first transfer means and allowing the same to proceed and turn at a rate not less than that of the transfer speed of the sheet metal in the first transfer means, (3) electromagnets provided near said second pulleys and along and above the lower path of the endless belt of the second transfer means, said electromagnets being adapted for attracting said sheet metal and permitting said sheet metal to proceed with said belts, (4) at least one sensing means provided adjacent said electromagnets adapted for being actuated when at least the rear end of the sheet metal reaches a position where it is not substantially subjected to the attracting power of said second pulleys and thereby eliminating the attracting power of said electromagnets and (5) discharging means provided below the lower path of the endless belts of said second transfer means and adapted for carrying said sheet metal to the next step at a rate not less than that of the transfer speed of the sheet metal at the first transfer means, said sheet metal having been separated and dropped from said belts as a result that said electromagnets have lost the attracting power by the actuation of the sensing means, the space or distance between said discharging means and the lower path of said endless belts being suCh that the attracting power of said electromagnets can not be substantially exerted over the sheet metal which has dropped down on said discharging means.
 2. An apparatus according to claim 1 in which the attracting means of the second pulleys at the second transfer means are permanent magnets provided in the periphery of said pulleys.
 3. An apparatus according to claim 1 in which said sensing means is at least one non-contact adjacent switch.
 4. An apparatus according to claim 1 in which the endless belts of the second transfer means are the magnet belts; the electromagnets provided along the lower path of the belts have, at least as a whole, one row of small rollers on each outer side thereof along the direction of travel of said belts, said rollers being capable of rotating on the sheet metal and forming a space between said sheet metal and said belts, said gap being such that the mere magnetic force of said belts is not enough to keep said sheet metal attracted thereto; and the sensing means is adapted for being actuated and eliminating the attracting power of said electromagnets when said sheet metal reaches the condition that it cannot be kept attracted by the belts by the single magnetic force of the belts. 